Check for null and undefined when getting type name for stack trace.

test/mjsunit/regress/regress-3718.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+"use strict";
+
+function getTypeName(receiver) {
+  Error.prepareStackTrace = function(e, stack) { return stack; }
+  var stack = (function() { return new Error().stack; }).call(receiver);
+  Error.prepareStackTrace = undefined;
+  return stack[0].getTypeName();
+}
+
+assertNull(getTypeName(undefined));
+assertNull(getTypeName(null));
+assertEquals("Number", getTypeName(1));
+assertEquals("String", getTypeName(""));
+assertEquals("Boolean", getTypeName(false));
+assertEquals("Object", getTypeName({}));
+assertEquals("Array", getTypeName([]));
+assertEquals("Custom", getTypeName(new (function Custom(){})()));